Fuse

ABSTRACT

The present invention relates to a fuse for improving the reliability and facilitating automation the process and, in this fuse, an inner cap 14 is provided between a glass tube 12 and a cap terminal 13; a passage 22 for ventilating the inside of the glass tube 12 is provided between the inner cap 14 and the glass tube 12; an end portion 15a of the fuse element 15 is taken out between the cap terminal 13 and the inner cap 14 through an element insertion hole 14b formed on a bottom plate 14a of the inner cap 14 in order to electrically connect the end portion 15a with at least the cap terminal 13; and the cap terminal 13 is fixed to the inner cap 14.

FIELD OF THE INVENTION

The present invention relates to a fuse. More particularly, the presentinvention relates to a reliable fuse which facilitates automation of theprocess.

BACKGROUND OF THE INVENTION

There is a tubular fuse as a safety device for protecting an electriccircuit from an excess current. As shown in FIG. 11, a generally-usedtubular fuse 1 is made up of a glass tube 2, a fuse element 3 arrangedin the glass tube 2 along an axial line of the glass tube 2, and a pairof cap terminals 4 (only one side is shown) fitted on both ends of theglass tube 2. Both ends of the fuse element 3 protrude and are solderedto the outside of the glass tube 2 through element insertion holes 4aformed to the respective cap terminals 4. This causes the fuse element 3to be directly supported in the center of the glass tube 2 by each capterminal 4 with a predetermined gap between the fuse element 3 and theglass tube 2. It is to be noted that both end portions 3a (indicated bya two-dot long and two short dashes line in the drawing) of the fuseelement 3 protruding from solder 5 after soldering are shaved off byusing a knife or the like.

In this tubular fuse 1, however, the solder 5 is piled up on the surfaceof the cap terminal 4 to fix the cap terminal 4 and the fuse element 3protruding from the element insertion hole 4a, which makes it difficultto automate the process and leads to the deteriorated productivity. Thatis, in case of external soldering, an advanced technique is required forsoldering for maintaining the quality of the fuse. For example, if thesolder is overflowed from the bottom to the outer peripheral surface ofthe cap, this can cause an imperfect contact with the fuse holder.Further, in order to obtain the sufficient strength, the soldering mustbe applied on the entire bottom surface of the cap around the elementinsertion hole 4a of the cap terminal 4 without making any unsolderedpart. Furthermore, when the soldering is not finished in one time and asoldering iron is again put to cover the unsoldered or insufficientpart, the hardened solder may be melted to loosen the fuse element 3.Only a skilled operator can, therefore, carry out the soldering and theautomation is not realized so far. However, the soldering causes thepoor working environment that may cause a flux or the like to begenerated, leading to the shortage of operators.

In addition, since the soldering is so applied as to cover the elementinsertion hole 4a of the cap terminal 4, the melted solder may bring theair therein and a cavity may be generated inside the solder 5 and abovethe element insertion hole 4a in particular, thereby preventing adesired strength from being obtained. Detection of this cavity is hardby the visual test, and hence it does not give a serious question tofusion of the fuse caused by the usual excess current if such a cavityexists. However, if a short-circuit or the like occurs near the fuse anda large current flows to cause interruption, the element may explode toblow the solder into pieces and to cause jet of an arc flame or gas oremission of metal powder.

Moreover, since the soldering is performed with the glass tube 2 beingerected in such a manner that the solder 5 is piled up from the top, themelted solder may run down from the element insertion hole 4a beforebeing hardened to wrap the fuse element 3 therein, and the length of theexposed part of the fuse element 3, i.e., the fuse length may becomeunequal to give the irregularity to the pre-arcing time/currentcharacteristic.

Additionally, as a tubular fuse enabling the automation of manufacture,there is one shown in FIG. 12. In this tubular fuse 6, both end portionsof the fuse element 3 are externally bent along the edges of the glasstube 2 and sandwiched between the glass tube 2 and a cap terminal 7 tobe fixed. According to this fuse structure, the fuse element 3 can betemporarily fixed by only fitting the cap terminal 7 and, if the solder5 is piled up inside the cap terminal 7 in advance, the soldering can beeffected by only heating in this state to fix the fuse element 3. Here,since the cap terminal 7 must be fitted with both the ends of the fuseelement 3 being caught on the edges of the glass tube 2 and beingstretched, the both ends are bent in the direction opposed to each otherin the diameter direction. The fuse element 3 is, therefore, obliquelyhoused in the glass tube 2.

In this tubular fuse 6, however, the fuse element 3 directly contactswith and is obliquely supported by the glass tube 2, and hence the fuseelement 3 may be brought into contact with the glass tube 2 in thevicinity of the edges of the glass tube. When the fuse element 3 isbrought into contact with the glass tube 2, the heat of the fuse element3 may be transferred to the glass tube 2 and fusion of the fuse element3 may be delayed.

Further, since the solder 5 is filled and directly fixed between theinner surface of the cap terminal 7 and the end surface of the glasstube 2, the inside of the glass tube 2 is sealed to disable ventilationwhen the cap terminal 7 is heated in order to melt the solder 5 providedon the inner surface of the cap terminal 7 and to fix the solder 5 tothe fuse element 3, the cap terminal 7 and the glass tube 2. An increasein the pressure inside the glass tube 2 causes application of the meltedsolder to be uneven so that the ununiformity be generated at a positionwhere the solder 5 is attached to the fuse element 3, and the length ofthe exposed part of the fuse element 3 thereby becomes unequal to givethe irregularity to the pre-arcing time/current characteristic. Also, insome cases, the solder 5 can not be attached and fixed to the fuseelement 3 on the edges of the glass tube 2, and the fuse element 3 is indirect contact with the glass tube 2, i.e., the fuse element 3 can notbe supported by the solder, which may damage the bent portions of thefuse element 3 or cause disconnection due to fatigue of a metal. Sincethe inside of the glass tube 2 is sealed, an increase in the innerpressure owing to explosion of the element can not be released at thetime of interruption caused due to a short-circuit accident or the like,and the glass tube 2 may explode or the cap terminal 7 may be blown out.The strength of the glass tube 2 or the joining force of the cap 7 mustbe considerably increased.

Furthermore, since the cap terminal 7 is fitted with the both ends ofthe fuse element 3 being stretched in the opposed directions along thediameter direction on the edges of the glass tube 2 in order to sandwichthe both ends between the glass tube 2 and the cap terminal 7, therelatively-large cap terminal 7 is inclined to the glass tube 2 and cannot be concentrically provided with respect to the glass tube 2. Inparticular, this tendency becomes prominent as the wire diameter of thefuse element 3 increases. The positions of the cap terminals 7 providedon both sides are, therefore shifted with respect to the glass tube 2 inthe opposed directions along the diameter direction by the thickness ofthe fuse element 3. As shown in FIG. 13, when the tubular fuse 6 isfitted to fuse clips, the point contact causes each cap terminal 7 to beheated and softens the hard solder 5 to loosen the stretched fuseelement 3, and the fuse element 3 is brought into contact with the glasstube 2, which leads to an imperfect fusion or the melted fuse clips.

Moreover, when mounting the tubular fuse 1 shown in FIG. 11 or thetubular fuse 6 shown in FIG. 12 on, e.g., a printed wiring board as afuse with a lead wire, such a fuse may be supplied to a solder tank of areflow furnace or the like and thereafter soldered on the printed wiringboard. In this case, if the temperature management of the reflow furnaceor the like is poor, the solder layer 5 fixing the fuse element 3becomes soft when the tubular fuse is heated, the stretched fuse element3 may be loosened to be brought into contact with the glass tube 2.

It is, therefore, an object of the present invention to facilitateautomation of the process and provide a reliable fuse.

DISCLOSURE OF THE INVENTION

To achieve this aim, a fuse according to the present invention ischaracterized in that: an inner cap fixed to a non-conductive tubularhousing body is provided between the tubular housing body and a capterminal which blocks an end portion of the tubular housing body; apassage for ventilating the inside of the tubular housing body isprovided between the inner cap and the tubular housing body; an endportion of a fuse element is taken out between the cap terminal and theinner cap through an element insertion hole formed substantially in thecenter of a bottom plate of the inner cap and electrically connected atleast to the cap terminal; and the cap terminal is fixed to the innercap.

Therefore, a double cap is fitted on the end portion of the tubularhousing body so that a means for fixing the cap terminal to the innercap, for example, the solder can spread between the end portion and thecap, and the inside of the tubular housing body is ventilated to enablea passage for avoiding an increase in pressure to be formed. Further,the cap terminal covers the solder (fixing member) blocking the innercap and the fuse element, and hence the blowout can be prevented fromoccurring due to the explosion energy of the interruption even though athin part is made in the solder. This facilitates automation of themanufacturing process and prevents an increase in pressure in thetubular housing body to avoid damage. In addition, although the fuseelement is stretched between the inner caps fitted at both the ends ofthe tubular housing body, both the ends of the fuse element are insertedinto the element insertion holes each formed at a position correspondingto substantially the center of the glass tube and thus the fuse elementis arranged sufficiently distant from the tubular housing body. Sincethe fuse element can be set sufficiently apart from the tubular housingbody, the heat of the fuse element can not be transferred to the tubularhousing body to avoid delay of fusion of the fuse element, therebyimproving reliability of the fuse. Furthermore, arrangement of the fuseelement distant from the tubular housing body can prevent the damagefrom being given to the fuse element due to a contact made between thefuse element and the end surface or the like of the tubular housing bodywhen assembling the fuse element, providing the fuse suitable forautomation of the manufacturing process.

The inner cap and the cap terminal according to the present inventionare fixed by a fixing means. Although a brazing material such as asolder, a conductive adhesive agent or the like can be exemplified asthis fixing means, the brazing material and the solder in particular canbe preferably used. In this case, the solder is accommodated on thebottom of the cap terminal in advance and melted by heating after thecap terminal is fitted on the inner cap in order to fix the capterminal, the fuse element and the inner cap with each other. Therefore,when manufacturing the fuse, soldering can be effected by only heatingusing a heater or a high-frequency induction furnace after assemblingall the constituent parts of the fuse. The solder spreads between thecap terminal and the inner cap to electrically connect the cap terminal,the inner cap and the fuse element. This can provide a fuse suitable forautomation of the process, thereby contributing to improvement of theproductivity.

Additionally, according to the present invention, the cap terminal andthe inner cap are joined to each other by press fitting. In this case,the fuse can be manufactured by simply press-fitting the cap terminal onthe inner cap with each end portion of the fuse element being fixed tothe inner cap. The fuse can be, therefore, suitable for automation ofthe assembling work to easily intend improvement of the productively,and reliability of the fuse can be enhanced.

Moreover, each end portion of the fuse element of the fuse is bent alongthe outer side surface of the inner cap and caught by the inner cap insuch a manner that the end portion is positioned and fixed between theinner cap and the cap terminal. In this case, when manufacturing thefuse, the cap terminal can be assembled with the end portion of the fuseelement being temporarily fixed. After assembling, the cap terminal andthe fuse element are brazed or bonded to the inner cap to complete theproduction of the fuse. Therefore, automation of the fuse assemblingwork can be facilitated to improve the productivity.

Further, in the fuse according to the present invention, each endportion of the fuse element is sandwiched and temporarily fixed betweenthe bottom plate of the inner cap and the cap. When manufacturing thefuse, the cap terminal can be thus assembled with each end portion ofthe fuse element being fixed in the inner cap, and the cap terminal isbrazed or bonded in the inner cap after the assembling work, completingthe production of the fuse. As similar to the above-described example,automation of the process can be thus facilitated and improvement of theproductivity can be easily intended.

In the fuse according to the present invention, each end portion of thefuse element is fixed to the bottom plate of the inner cap. Althoughspot welding, brazing, laser welding, fixing using a conductive adhesiveagent and others can be exemplified as this fixing means, application ofspot welding is preferable especially. In this case, with each spotelectrode being put on the inner cap, flowing the electric currentbetween the respective spot electrodes ensures the fuse element to befixed and electrically connected to the inner cap. That is, fuse elementcan be easily fixed to the inner cap to further improve theproductivity. Since a joint part of the fuse element and the inner capfixed by the spot welding has a melting point higher than that obtainedby soldering, the fuse element can not be loosened even though the heatmanagement of the solder tank is poor and the solder is softened. It ispreferable that the position to which the end portion of the fuseelement is fixed is the bottom plate of the inner cap and that it is aninclined surface of the bottom plate depressed toward the tubularhousing body in particular. In this case, when the tubular housing bodyis inclined toward the fuse element with the fuse element being insertedinto the tubular housing body having the inner cap fixed thereto at theboth ends, the fuse element is brought into contact with the inclinedsurface of the bottom plate of the inner cap. That is, the fuse elementcan become parallel with the bottom plate of the inner cap without beinglargely bent. Therefore, it is possible to suppress fatigue of a metalgenerated at a bent part by a temperature cycle which repeatedly affectson the fuse element, thus improving durability and reliability of thefuse.

In addition, fixation of the fuse element to the inner cap and fixationof the cap terminal to the inner cap can be done by using differentmeans. The fuse element can be, therefore, successfully fixed to theinner cap even though the fixed state of the cap terminal with respectto the inner cap becomes loose, preventing the fuse element from beingloosened.

Furthermore, in the fuse according to the present invention, a part ofthe fuse element which is close to the tip from the fixing position tothe inner cap is positioned in the vicinity of the indent of the bottomplate of the inner cap. Accordingly, the part of the fuse element whichis close to the tip from the fixing part to the inner cap does not enterthe space between the outer peripheral surface of the inner cap and theinner peripheral surface of the cap terminal, and the inner cap, the capterminal and the glass tube can be concentrically arranged. Thus, thefuse can be straightly mounted to the fuse clips, and their contact areacan be sufficiently assured, thereby obtaining the good conductivestate.

Moreover, in the fuse according to the present invention, theventilation passage between the inner cap and the tubular housing bodyis sealed by the solder flowed out from the element insertion holeformed on the bottom plate of the inner cap. In this case, production ofa micro-fuse can be automated.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view showing a primary part of a firstembodiment of a tubular fuse to which the present invention is applied;FIG. 2 is a cross-sectional view showing a primary part of a secondembodiment of the tubular fuse to which the present invention isapplied; FIG. 3 is a cross-sectional view showing a primary part of athird embodiment of the tubular fuse to which the present invention isapplied; FIG. 4 is a cross-sectional view showing a primary part of afourth embodiment of the tubular fuse to which the present invention isapplied; FIG. 5 is a cross-sectional view showing a fifth embodiment ofa fuse to which the present invention is applied; FIG. 6 is a schematicstructural view showing a part of the process for manufacturing the fuseillustrated in FIG. 5, with a fuse element being inserted into a glasstube and each inner cap; FIG. 7 is a schematic structural view showing apart of the process for manufacturing the fuse illustrated in FIG. 5 inorder to explain how to spot-weld the fuse element to the inner cap;FIG. 8 is a cross-sectional view showing a primary part of a sixthembodiment of the fuse to which the present invention is applied; FIG. 9is a cross-sectional view showing a primary part of a seventh embodimentof a fuse to which the present invention is applied; FIG. 10 is aschematic structural view showing a part of the process formanufacturing the fuse illustrated in FIG. 9 in order to explain how tobend an end of the fuse element; FIG. 11 is a cross-sectional view of aprior art tubular fuse; FIG. 12 is a cross-sectional view of anotherprior art tubular fuse; and FIG. 13 is a plan view in which the tubularfuse illustrated in FIG. 12 is mounted to fuse clips.

BEST MODES FOR EMBODYING THE INVENTION

The structure of the present invention will now be described in detailhereunder in connection with illustrative best modes.

FIG. 1 shows a first embodiment of a tubular fuse according to thepresent invention. The tubular fuse 11 is mounted to non-illustratedfuse clips to be used and comprises: a non-conductive tubular housingbody, e.g., a glass tube 12; an inner cap 14 adhered to each of bothends of the glass tube 12; a cap terminal (external cap) 13 fitted onthe inner cap 14 to function as a fuse terminal; a fuse element 15having both ends each taken out between the cap terminal 13 and theinner cap 14 and caught by the inner cap 14; and a means forelectrically connecting the inner cap 14 and the cap terminal 13, i.e.,solder 17, with a ventilation passage 22 being provided between theinner cap 14 and the glass tube 12.

That is, as similar to the cap terminal 13, the inner cap 14 isconductive and a bottom plate 14a thereof is molded into a conical shapewhose head portion is cut off. In other words, the bottom plate 14a ofthe inner cap 14 conically protrudes towards the outside of the glasstube 12. An element insertion hole 14b is formed on the inner cap 14 ata position apart from the glass tube 12, i.e., substantially in thecentral position of the bottom plate 14a. The element insertion hole 14bis formed to be sufficiently large as compared with the fuse element 15.

The inner cap 14 is fitted on an end of the glass tube 12 and fixed byan adhesive agent 16. The adhesive agent 16 is applied on apredetermined area of the glass tube 12 in the circumferentialdirection, e.g., an area corresponding to approximately 2/3 of the same.Therefore, in a part where no adhesive agent 16 is applied, a gap isgenerated between the inner cap 14 and the glass tube 12, and this gapserves as the ventilation passage 22 for ventilating the inside of theglass tube 12. However, the area on which the adhesive agent 16 isapplied is not restricted to that described above, and it can be anyarea as long as a passage area which can prevent the inner cap 14 fromfalling and is sufficient for ventilating the inside of the glass tube12 can be obtained. Also, it is needless to say that the adhesive agent16 may be applied on several points so as to form dots or lines.

A fuse element (fusible metal wire material) 15 is obtained by applying,e.g., silver plating on copper and housed in the glass tube 12. An endportion 15a of the fuse element 15 is taken out between the cap terminal13 and the inner cap 14 through the element insertion hole 14b of theinner cap 14 and sharply bent along the outer peripheral surface of thebottom plate 14a of the inner cap 14. As the fuse element 15, thosehaving various kinds of composition or structure can be appropriatelyselected in accordance with the application of the fuse.

The cap terminal 13 for covering the end portion of the glass tube 12 isfitted on the inner cap 14 and fixed to the inner cap 14 together withthe end portion 15a of the fuse element 15 by, e.g., soldering. That is,a solder which is heated and melted after the cap terminal 13 is fittedon the inner cap 14 and spreads between the cap terminal 13 and theinner cap 14 is provided inside the cap terminal 13. This ensures theend portion 15a of the fuse element 15 to be electrically connected withthe cap terminal 13 and the inner cap 14.

It is to be noted that the inner cap 14 and the cap terminal 13 arefitted to each of both the ends of the glass tube 12 and support theboth end portions 15a of the fuse element 15. Further, the glass tube 12is so set as to have predetermined length and diameter in compliancewith standards required by consumer countries, users and others.

The tubular fuse 11 is manufactured in the following manner.

The respective inner caps 14 are first fitted on the both end portionsof the glass tube 12 and fixed by using the adhesive agent 16. The fuseelement 15 is then inserted through the element insertion hole 14b ofthe inner cap 14, and both the end portions 15a of the fuse element 15are bent along the conical bottom plate 14a. Here, the fuse element 15which is so cut to a desired length in advance may be prepared, or itmay be continuously drawn out and cut by a bending means. Since the fuseelement 15 has rigidity to some extent and plastically deforms when bentin the substantially-V shape, the fuse element 15 is temporarily fixedin such a manner that it is stretched between the respective inner caps14. That is, in this state, the fuse element 15 does not come off unlessit receives a large external force, and the cap terminal 13 can befitted with the fuse element 15 being stretched as will be describedlater.

On the other hand, a predetermined amount of solder 17 is put on theinside of the cap terminal 13 in advance. This cap terminal 13 is thenfitted on the inner cap 14 having the fuse element 15 being temporarilyfixed thereto and the circumference of the cap terminal 13 is heated.The solder 17 inside the cap terminal 13 is melted by heating andspreads between the cap terminal 13 and the inner cap 14 to fix the capterminal 13 and the fuse element 15 to the inner cap 14.

In this manner, soldering can be effected by melting a predeterminedamount of the solder 17 supplied in advance by utilizing an externalheat source after assembling the respective constituent parts, and henceautomation of the assembling work can be facilitated. Further, whenautomating the work, since the fuse element 15 is stretched between therespective inner caps 14 to fix both the ends, it is possible to preventa damage due to contact with the end surface of the glass tube 12 fromoccurring. Moreover, the aim of the invention can be assuredly achievedbecause soldering is performed for only filling the space between thecap terminal 13 and the inner cap 14, and covering the outside with thecap terminal 13 does not lead to the blowing of the fuse at the time ofinterruption explosion even though a thin part is formed on the film ofthe solder 17.

In addition, since the element insertion hole 14b of the inner cap 14 islargely formed for the fuse element 15, the fuse elements 15 havingvarious kinds of thickness can be used to the same inner cap 14, the capterminal 13 and the glass tube 12.

In this tubular fuse 11, since the fuse element 15 can be arrangedsubstantially in the center of the glass tube 12 sufficiently apart fromthe glass tube 12 by the inner cap 14, the fuse element 15 can beprevented from coming into contact with the glass tube 12, and the heatof the fuse element 15 can not be transferred to the glass tube 12 whenthe current flows, thereby avoiding the imperfect fusion of the fuseelement 15 when a current value reaches a specified current value.

Further, the inside of the glass tube 12 is ventilated through thepassage 22 as described above. This can prevent the pressure inside theglass tube 12 from abnormally increasing to avoid a damage given on theglass tube 12 when the over current flows through the tubular fuse 11 tocause the fuse element 15 to instantaneously have a high temperature andto be fused (interruption explosion).

FIG. 2 shows another embodiment of the tubular fuse according to thepresent invention. In the fuse 18 according to this embodiment, thebottom plate 14a of the inner cap 14 is not molded into a conical shapewhose head portion is cut off but formed to have a flat surface. In caseof this tubular fuse 18, there is adopted the inner cap 19 whose bottomplate 19a has a flat disc form, and both the ends of the fuse element 15are bent at a right angle so that the fuse element 15 be caught by thebottom plate 19a of the inner cap 19. The fuse element 15 is sandwichedbetween the bottom plate 19a of the inner cap 19 and the bottom of thecap terminal 13 after melting the solder 17. Therefore, the fuse element15 can not be loosened even when the solder 17 is slightly melted andsoftened by the heat from the reflow furnace at the time of mounting thefuse.

FIG. 3 shows a third embodiment according to the present invention. Thefuse 20 according to this embodiment has such a structure as that theend portion 15a of the fuse element 15 is previously fixed to the bottomplate 19a of the inner cap 19 before fitting the cap terminal 13 to theinner cap 19. As a method for fixing the end portion 15a of the fuseelement 15 to the inner cap 19, it is possible to adopt, e.g., spotwelding using an inverter spot welder or a transistor spot welder,welding using a laser beam to be irradiated, or fixing using aconductive adhesive agent. It is, however, necessary that the fixedstate must not be cancelled at a temperature higher than a melting pointof the solder 17. It is to be noted that reference character S in thedrawing designates a point where the spot welding is carried out.

Soldering does not have to be used to join the cap terminal 13 with theinner cap 19, and as shown by, e.g., the tubular fuse 21 in FIG. 4, thecap terminal 13 may be press-fitted to be fixed to the inner cap 19whose bottom plate 19a has the end portion 15a of the fuse element 15spot-welded thereto. In this case, a space, to which no adhesive agent16 is applied, between the inner cap 19 and the glass tube 12 may serveas the passage 22, or a groove may be provided on the inner surface ofthe cap terminal 13 or the outer surface of the inner cap 19 to form thepassage 22 between the cap terminal 13 and the inner cap 19.

Although the element insertion holes 14b and 19b are formedsubstantially in the center of the bottom plates 14a and 19a in theabove respective inner caps 14 and 19, positions at which the elementinsertion holes 14b and 19b are formed are not restricted to the centerof the bottom plates 14a and 19a and they can be of course formed atpositions shifted from the center as long as the fuse element 15 can bearranged sufficiently apart from the glass tube 12.

The above has described that the soldering is a method for fixing thecap terminal 13 to the inner caps 14 and 19, but the method is notrestricted to the soldering and a brazing, a conductive adhesive agentor the like may be used. That is, the brazing or the conductive adhesiveagent, which spreads between the cap terminal 13 and the inner caps 14and 19 after the cap terminal 13 is fitted on the inner caps 14 and 19,may be provided inside the cap terminal 13 before fitting the capterminal 13 to the inner caps 14 and 19.

It is preferable that the inner caps 14 and 19 are conductive but do nothave to be conductive.

Furthermore, although the end portion 15a of the fuse element 15 iselectrically connected to the cap terminal 13 and the inner cap 14 bysoldering in the above description, the end portion 15a may beelectrically connected at least to the cap terminal 13.

FIG. 5 shows a fifth embodiment of a fuse according to the presentinvention. In the tubular fuse 31 of this embodiment, the bottom plate34a of the inner cap 34 conically protrudes toward the inside of theglass tube 32 to form an indent on the bottom of the inner cap 34. Inother words, the bottom plate 34a of each inner cap 34 conicallyprotrudes toward the glass tube 32 to form an inclined surface 34c. Theend portion 35a of the fuse element 35 is fixed to this inclined surface34c by, e.g., spot welding. However, the fixing method is notnecessarily limited to the spot welding and it may be, e.g., fixingusing a conductive adhesive agent or brazing. In addition, a part of thefuse element 35, which is close to the tip from a fixing position S withrespect to the inner cap 34, is cut short and set inside the outerdiameter of the bottom plate 34a of the inner cap 34 for example. Thepart of the fuse element 35, which is close to the tip from the fixingposition S with respect to the inner cap 34, does not project toward theouter peripheral side of the inner cap 34.

It is to be noted that the cap terminal 33 is fixed to the inner cap 34by the solder 37. However, the method for fixing the cap terminal 33 tothe inner cap 34 is not limited to the solder 37, and a conductiveadhesive agent or the like may be used. When brazing is used to fix theend portion 35a of the fuse element 35 to the inclined surface 34c andfix the cap terminal 33 to the inner cap 34, it is preferable that abrazing material for joining the fuse element 35 to the inner cap 34 hasa melting point higher than that of a brazing material for joining thecap terminal 33 to the inner cap 34.

This fuse 31 is manufactured in the following manner, for example.

In the first place, the inner cap 34 is respectively fitted to both theends of the glass tube 32 and the adhesive agent 36 is used to fix them.In this case, adjusting a fitting quantity of the inner cap 34 canabsorb the irregularity in length of the glass tube 32 to make thelength of the fuse 31 uniform.

The fuse element 35 is then inserted through the element insertion hole34b of each inner cap 34 and the glass tube 32. As shown in FIG. 6, thefuse element 35 is gripped by chucks 39 and 40 and stretched straightly.Subsequently, the glass tube 32 is inclined with respect to the fuseelement 35 and the fuse element 35 is brought into contact with thebottom plate 34a of the inner cap 34 in parallel with each other asshown in FIG. 7. In this state, one spot electrode 41 is put on theouter peripheral surface of the inner cap 34 and the other spotelectrode 42 is put on the fuse element 35 to perform the spot welding.This ensures the fuse element 35 to be fixed to the conductive inner cap34 so that they can be electrically connected to each other. Then, witha tension being applied to the fuse element 35, the part of the fuseelement 35 which is close to the tip from the fixing position S relativeto the inner cap 34 is cut. At this time, the part of the fuse element35 which is close to the tip from the fixing position S is shortened bycutting the part close to the fixing position S and it is thus arrangedinside the indent of the bottom plate 34a of the inner cap 34. Thestructure is not restricted thereto and, as shown in FIG. 8, a cutter 43for cutting the fuse element 35 may be used for bending the fuse element35 inwardly so that the part of the fuse element 35 which is close tothe tip from the fixing position S can be accommodated inside the outerdiameter of the bottom plate 34 of the inner cap 34, or more preferably,it can be accommodated in the indent portion of the bottom plate 34a.That is, after the fuse element 35 is nipped by the cutter 43 to be bentand the cutter 43 is thereafter used to cut the fuse element 35, orafter the cutter 43 is first used to cut the fuse element 35, the freeend of the fuse element 35 can be pushed and bent by the cutter 43. Inthis case, the tip of the fuse element 35 is bent toward the center ofthe bottom plate 34a of the inner cap 34 so that it can be put insidethe outer diameter of the bottom plate 34a as in the seventh embodimentillustrated in FIG. 9, which can prevent the cap terminal 33 from beinginclined toward the inner cap 34. The spot welding and cutting aresimilarly applied to the end portion 35a of the fuse element 35 on theopposite side.

On the other hand, a predetermined amount of solder 37 is previouslyprovided inside the cap terminal 33. The cap terminal 33 is then fittedon the inner cap 34 to which the fuse element 35 is fixed, and the lowercap terminal 33 is heated with the glass tube 32 being erected. As aheating method, there is a method using a heater or another methodutilizing a high-frequency induction furnace, for example. The solder 37inside the cap terminal 33 is melted by heating and spreads between thecap terminal 33 and the inner cap 34. At the same time, the solder 37also moves to the glass tube 32 while pushing the gas in the glass tube32 through the passage 38 and fills the gap between the cap terminal 33and the inner cap 34 to fix them. This ensures the cap terminal 33, theinner cap 34 and the fuse element 35 to be electrically connected.

Here, if an amount of the solder 37 provided inside the cap terminal 33in advance is determined so that the solder 37 can not flow out from theelement insertion hole 34b of the bottom plate 34a, the fixed state ofthe fuse element 35 can be stable. That is, since the solder 37 ismelted with the glass tube 32 being erected and the cap terminal 33being positioned on the lower side, the height (liquid level) forimpounding the melted solder 37 becomes constant, and the height of theexposed part of the fuse element 35 can be fixed. Further, the solder 37flowed out from the element insertion hole 34b is stored inside theinner cap 34 by the gravity even if the amount of the solder 37 providedinside the cap terminal 33 is unequal to some extent, and the exposedportion of the fuse element 35 is not covered too much, thus making thelength of the exposed portion of the fuse element 35 constant.

Further, after spot-welding the fuse element 35 to the inner cap 34provided on each end of the glass tube 32, the cap terminal 33 is fittedand the soldering is performed by melting a predetermined amount of thesolder 37 accommodated in the inside of the cap terminal 33 in advanceby utilizing an external heat source when the assembling is completed,which facilitates automation of the process, improving the productivity.Further, the soldering is completed by filling the space between the capterminal 33 and the inner cap 34, and hence the aim can be achieved.Even if a thin part is generated in the solder, it is covered with thecap terminal 33 and it can not be blown out by the breaking explosion.

Moreover, bubbles do not remain in the solder 37 and a cavity isprevented from being generated to maintain the good fixed state of theinner cap 34 and the cap terminal 33. When the work is automated, sincethe fuse element 35 is stretched between the respective inner caps 34,the fuse element 35 does not come into contact with the end surface ofthe glass tube 32, avoiding the damage. Therefore, the fuse 31 suitablefor automating the manufacturing process can be provided.

As different from the soldering for fixing the cap terminal 33 to theinner cap 34, the end portion 35a of the fuse element 35 is fixed to theinclined surface 34c of the inner cap 34 by the spot welding, and hencethe fuse element 35 can not be loosened even though the heat is appliedand the hardened solder 37 is softened. For example, when embodied as afuse having a lead wire, the fuse 31 is put on a printed wiring board orthe like and sent to the reflow furnace in this state for the mountingprocess. Here, the solder 37 may be softened if the heat management ofthe solder tank is poor. However, according to the fuse 31 of thisinvention, since the end portion 35a of the fuse element 35 is fixed tothe inner cap 34 by the spot welding even if the solder 37 is softened,the fuse element 35 can not be loose and the contact between the fuseelement 35 and the glass tube 32 can be avoided. In addition, the fuseelement 35 can be arranged sufficiently apart from the glass tube 32,and hence the fuse element 35 can be prevented from coming into contactwith the glass tube 32 to assure the operation of the fuse 31, therebyimproving the reliability.

Moreover, since the fuse element 35 is spot-welded to the inclinedsurface 34c of the inner cap 34, the fuse element 35 can be fixed to theinner cap 34 without largely bending the fuse element 35, the solder 37can excellently spread to wrap the end portion 35 of the fuse element35, and the temperature cycle repeatedly acting on the fuse element 35can suppress fatigue of the metal generated in the bent portion,enhancing the durability and the reliability of the fuse 31.

Since the part of the fuse element 35 close to the tip from the fixingposition S relative to the inner cap 34 is cut short and this part closeto the tip is not sandwiched between the outer peripheral surface of theinner cap 34 and the inner peripheral surface of the cap terminal 33,the thick fuse element 35 such as a rush proof fuse (wound thick fuse)can be thus used, and automation of assembling process is also possiblein this case.

Since the end portion 35a of the fuse element 35 is not sandwichedbetween the outer peripheral surface of the inner cap 34 and the innerperipheral surface of the cap terminal 33, the cap terminal 33, theinner cap 34 and the glass tube 32 can be concentrically arranged. Thisensures the both cap terminals 33 to be coaxially provided, and they canbe straightly mounted to the fuse clips, enabling their contact part tobe a surface contact.

In this fuse 31, since the fuse element 35 can be provided substantiallyin the center of the glass tube 32 sufficiently apart from the glasstube 32 by the inner cap 34, the fuse element 35 can be prevented fromcoming into contact with the glass tube 32, and transfer of the heatfrom the fuse element 35 to the glass tube 32 can be avoided whenturning on electricity, thereby evading the delay of fusion of the fuseelement 35 when the current value reaches a specified current value.

Further, the inside of the glass tube 32 is ventilated through thepassage 38 between the inner cap 34 and the glass tube 32 as describedabove. Therefore, even if the excess current flows to the fuse 31 due toa short-circuit accident or the like and fusion occurs so that the fuseelement 35 may explode, the air in the glass tube 32 passes through thepassage 38 to be emitted, and an abnormal increase in the pressureinside the glass tube 32 can not occur.

The above has described the preferred embodiments according to thepresent invention, but the invention is not restricted thereto, andvarious modifications and other embodiments are possible within the truescope and spirit of the invention.

For example, although description has been given mainly as to a fusehaving a structure such that the ventilation passages 22 and 38 areprovided between the glass tubes 12 and 32 and the inner caps 14 and 34in the above respective embodiments, the invention is not restrictedthereto. As in the seventh embodiment illustrated in FIG. 9, a sealedtype fuse is also possible by making an amount of the solder 37previously provided inside the cap terminal 33 larger than an amount ofthe solder 37 used in the fuse 31 shown in FIG. 5 and sealing the insideof the glass tube 32 after soldering the inner cap 34 and the capterminal 33. This fuse is surface-mounted on the printed wiring boardand generally referred to as a micro-fuse. This micro-fuse employs asmall square tube made of ceramics instead of the glass tube and adoptsthe sealed structure in preparation for the cleaning process after themounting process. Since the over current does not flow during theinterruption because the fuse is used on the circuit side, i.e., thesecondary side, the interruption explosion can not occur and the sealedstructure can be used without hindrance. In this fuse, the solder 37previously provided inside the cap terminal 33 is so determined as tohave an amount such that the solder 37 flows out from the elementinsertion hole 34b and reaches to cover the ventilation passage 38 whenthe cap terminal 33 is fitted to the inner cap 34. With the cap terminal33 being fitted on the inner cap 34 provided on each end to which thefuse element 35 is spot-welded, the glass tube 32 is erected and onlythe lower cap terminal 33 is heated. The melted solder 37 rises andfills the indent 34a on the bottom surface of the inner cap 34 while thegas in the glass tube 32 flows out from the ventilation passage 38, andthe solder 37 overflows from the element insertion hole 34b. Theoverflowed solder 37 moves down on the inner surface of the inclinedsurface 34c of the inner cap 34 and flows into the passage 38. That is,the melted solder 37 flows to the inner side of the bottom plate 34afrom the element insertion hole 34b to cover the passage 38. In thisstate, when the solder 37 is hardened, the inside of the glass tube 32is sealed. Here, the solder 37 flows from the element insertion hole 34bof the bottom plate 34a toward the inner side of the bottom plate 34a,which fixes the fixing position S of the fuse element 35 relative to theinner cap 34 from both the inside and the outside, thereby furtherstrengthening the fixing state between the fuse element 35 and the innercap 34.

Further, the element insertion hole 34b does not have to be formedsubstantially in the center of the bottom plate 34a of the inner cap 34,and the element insertion hole 34b may be formed at an eccentricposition of the bottom plate 34a as long as the fuse element 35 can bearranged sufficiently apart from the glass tube 32 or more preferably itcan be inserted into the central position of the glass tube 32.

Although the glass tube is exemplified as the tubular housing body inthis embodiment, the invention is not restricted thereto, and anynon-conductive member can be used.

Moreover, the above has described the fuse which can be used whenmounted to the fuse clips, but the fuse to which the present inventionis applied is not restricted to this type of fuse, a wire leaded fusewhich can be directly mounted on a printed wiring board or the like bydirectly connecting the lead wire to the cap terminal can be of courseembodied.

We claim:
 1. A fuse comprising:a non-conductive tubular housing body; acap terminal covering an end portion of the tubular housing body; aninner cap having a bottom plate, the inner cap being provided betweenthe tubular housing body and the cap terminal, the inner cap being fixedto the tubular housing body; a passage for ventilating an inside of thetubular housing body, the passage being provided between the inner capand the tubular housing body and connecting the inside of the tubularhousing body to an outside of said tubular housing body; an elementinsertion hole formed substantially in a center of the bottom plate ofthe inner cap; and a fuse element having an end portion, the end portionof the fuse element being taken out between the cap terminal and theinner cap through the element insertion hole and being electricallyconnected at least to the cap terminal, while the cap terminal beingfixed to the inner cap.
 2. A fuse according to claim 1, wherein theinner cap and the cap terminal are fixed by a fixing means.
 3. A fuseaccording to claim 2, wherein the fixing means is a solder which isprovided on a bottom of the cap terminal in advance and melted byheating after fitting the cap terminal to the inner cap in order to fixthe cap terminal, the fuse element and the inner cap with each other. 4.A fuse according to claim 1, wherein the cap terminal and the inner capare fixed by press-fitting.
 5. A fuse according to claim 1, wherein theend portion of the fuse element is bent along an outer peripheralsurface of the inner cap and caught by the inner cap.
 6. A fuseaccording to claim 1, wherein the end portion of the fuse element issandwiched between the bottom plate of the inner cap and the capterminal to be temporarily fixed.
 7. A fuse according to claim 1,wherein the end portion of the fuse element is fixed to the bottom plateof the inner cap.
 8. A fuse according to claim 7, wherein each of theinner caps has the bottom plate including an inclined surface depressedtoward the inside of the tubular housing body and the end portion of thefuse element is fixed to the inclined surface.
 9. A fuse according toclaim 7, wherein the end portion of the fuse element is fixed to thebottom plate of the inner cap by spot welding.
 10. A fuse according toclaim 8, wherein a part of the fuse element close to a tip of the fuseelement from a fixing position relative to the inner cap is positionedin a vicinity an indent of the bottom plate of the inner cap.
 11. A fuseaccording to claim 1, wherein the ventilation passage between the innercap and the tubular housing body is sealed by using solder flowed outfrom the element insertion hole formed on the bottom plate of the innercap.